Various prior fabrics and braided materials have been used in the manufacture of composite articles. For example, two-dimensional fabrics, whether braided, woven, or made by non-woven processes, are typically deployed in the manufacture of a composite part in multiple layers of tow material to build up predetermined thicknesses of material that may vary throughout the composite part. Conventional three-dimensional fabrics have been similarly used in the manufacture of composite parts.
In this disclosure we use the term “tow” as a cluster or grouping of materials that extend together in a principal direction as a unit. Tows may be one fiber or a plurality of fibers. Tows may include monofilaments, multiple filaments or combinations of monofilament and multiple filament strands, and may be staple or spun materials. Tow materials can have a variety of cross-sectional shapes, including but not limited to, generally circular, ellipsoidal, triangular and flat tape shapes. Fibers forming a tow may be twisted, twined, braided or otherwise shaped or combined, or may extend contiguously without being twisted or twined together. Fibers forming tows may be coated with resin or other coating to facilitate braiding and/or subsequent processing. A tow can include any combination of materials and material forms. As examples, a tow may include all carbon materials, a combination of carbon and thermoplastic materials, or a combination of aramid and glass materials. Other combinations of tow materials are known and used in composite structures and may be used in the present invention.
Prior conventional braiding machines include several variations generally of a circular configuration for production of two-dimensional braids, and various configurations for production of three-dimensional braids. Prior braiding machines for production of two-dimensional braid structures typically used synchronized horn gears supported by a circular ring. The horn gears accept and guide tow-bearing devices, commonly called tow carriers, for some portion of their rotation. The ring supporting the horn gears has a track or another means engaging guide elements on the tow carriers to transfer the carriers from one horn gear to an adjacent horn gear according to a predetermined braid manufacturing plan. In the prior braiders, typically one group of carriers moved along the ring in a generally clockwise direction and one group moved along the ring in the opposing, generally counterclockwise direction. The tow carriers delivered tow material to a former plate or mandrel to help control the braid formation. The axis of the braid formation mandrel in prior conventional braiders was usually collinear with the axis of the braid machine and manufactured braided article. Braid structures from prior conventional braiders are typically formed in the tubular shape and either made to lie flat for collection for post-processing or shipping or are singly- or doubly-slit to form lay-flat fabrics.
Prior three-dimensional structures have tows providing cross-thickness load paths, which is in the radial direction in a tubular sleeve. Three prior methods of forming three-dimensional braids include (1) the 4-step process, (2) the two-step process, and (3) the multilayer interlock braiding process. The 4-step process is also known by other names such as row-and-column braiding, Omniweave, Magnaweave, and through-the-thickness braiding. The 4-step braiding machine has a flat or cylindrical bed moving tow carriers from predetermined point-to-point locations on a grid of rows and columns. The 4-step process is exemplified by U.S. Pat. No. 4,312,261 Florentine. The two-step three-dimensional braiding process includes a relatively large number of fixed tow carriers that deliver tows into an axial direction of the braided structure and a fewer number of moving tow carriers as compared to 4-step braiding. The two-step process is exemplified by U.S. Pat. No. 4,719,837 McConnell et al. The multilayer interlocking three-dimensional braiding process uses a braiding machine that moves tow carriers in a way similar in configuration to a circular braiding machine used to manufacture conventional two-dimensional braids. However, in the multilayer interlocking process, the horn gears are arranged in a Cartesian grid or in concentric circular paths around the longitudinal axis of the braiding machine. The multilayer interlocking process is exemplified by U.S. Pat. No. 5,388,498 Dent et al and U.S. Pat. No. 5,501,133 Brookstein et al.
One common characteristic of prior conventional two- and three-dimensional braiding machines is that they are all designed for using a certain number of tow carriers, limiting the braid that can be produced to those having the same or fewer number of tows than the maximum number of tow carriers provided by the braider. Particularly, most commercially available braiders are limited to 144 tow carriers. Some prior machines have been configured for several types of braid structures within limits where some types of braid structure utilize fewer than the maximum numbers of tow carriers, such as producing tape braids on a conventional circular braiding machine where a limited number of carriers travel over a portion of the arc of travel.
Typically, braid manufacturers have employ limited numbers of machines of desired maximum numbers of tow carriers. The manufacturer's products are limited to by the capacity and arrangement of the braiders, and the limited configurability of conventional machines has limited the range of products that a manufacture may produce.